1. Field of the Invention
The present invention relates to an electroluminescence element.
2. Description of the Related Art
Electroluminescence elements which are formed on normal glass substrates have two glass substrates: a glass substrate on which a light-emitting layer is formed; and a glass substrate on which a moisture absorbent material is formed. The two glass substrates are bonded together along their periphery with a sealing resin.
In general, an electroluminescence element emits light by applying a current in a very thin light-emitting layer as thin as about 100 nm. Thus, if the light-emitting layer has fine concaves and convexes on its surface, leakage may occur between an anode and a cathode in the element. Therefore, an anode picture-element pattern, which is formed in each picture element on active circuits, such as thin film transistors, needs to be designed and manufactured with flatness of a nanometer level. Such an electroluminescence element is characterized by its high susceptibility to physical damage due to contact, force or impact.
On the other hand, attempts have been made to form a thin film device on a light-weight, highly flexible substrate such as a plastic substrate, instead of on a glass substrate. Thus, flexible displays using electroluminescence elements have attracted great attention.
For example, Japanese Published Patent Application No. 2005-339863, Japanese Published Patent Application No. 2003-77679, or the like is disclosed as a flexible display using an electroluminescence element.
Conventional electroluminescence elements formed on flexible substrates generally use two kinds of element structures.
The first element structure is a structure in which two plastic substrates are bonded together. In this structure, two plastic substrates, that is, two flexible substrates, are bonded together. Thus, when bending the laminate of the substrates, the surface of a light-emitting layer is brought into contact with the opposing substrate, because the substrates are fixed with a sealing resin along their periphery. Such contact can destroy the very sensitive light-emitting layer, causing problems such as leakage defects and defective light-emission. In addition to bending the laminate of the substrates, if a force is applied to the surfaces of the plastic substrates, the light-emitting layer is brought into contact with the opposing substrate due to deformation of the plastic substrates, thereby causing similar problems such as leakage defects and defective light-emission.
The second element structure is formed by a plastic substrate having TFTs (Thin Film Transistors), an interlayer insulating film, an anode, an insulating film for insulating picture elements from each other, a light-emitting layer, a cathode, and a sealing film.
Such an electroluminescence element uses a sealing film such as a CVD (Chemical Vapor Deposition) film instead of the sealing substrate, and is advantageous in that the electroluminescence element can be formed by using only one flexible substrate. However, an organic material, such as a plastic substrate and a light-emitting layer for use in an electroluminescence element, generally agglomerates to form foreign particles during manufacturing, thereby forming protrusions. Leakage defects tend to be generated if such protrusions formed by the foreign particles are produced in a portion insulated by the very thin light-emitting layer. Such leakage defects are repaired by a so-called laser repair process, i.e., a process of applying laser light to remove electrodes in the regions corresponding to the protrusions. However, since the sealing resin is located directly above the cathode, performing the laser repair process on a conventional electroluminescence element having an element structure destroys the sealing film, causing problems such as a failure to accurately remove the electrodes.